This application relates generally to microelectromechanical systems, and ore particularly to methods for affirming a switched status of MEMS-based devices.
In recent years, increasing emphasis has been made on the development of techniques for producing microscopic systems that may be tailored to have specifically desired electrical and/or mechanical properties. Such systems are generically described as microelectromechanical systems (MEMS) and are desirable because they may be constructed with considerable versatility despite their very small size. One example of a MEMS component structure is a micromirror, which is generally configured to reflect light from at least two positions. Such micromirrors find numerous applications, including as parts of optical switches, display devices, and signal modulators, among others.
In many applications, such as may be used in fiber-optics applications, such MEMS-based devices may include hundreds or even thousands of micromirrors arranged as an array. Within such an array, each of the micromirrors should be accurately aligned with both a target and a source. Such alignment is generally complex and typically involves fixing the location of the MEMS device relative to a number of sources and targets. If any of the micromirrors is not positioned correctly in the alignment process and/or the MEMS device is moved from the aligned position, the MEMS device will not function properly.
MEMS devices provide for individual movement of each of the micromirrors. An example is provided in FIGS. 1A–1C illustrating a particular MEMS micromirror structure that may take three positions. The micromirror structure illustrated in FIGS. 1A–1C is of the torsion-beam type. Each micromirror includes a reflective surface 116 mounted on a micromirror structural film 112 that is connected by a structural linkage 108 to an underlying substrate 104. Movement of an individual micromirror is controlled by energizing actuators 124a and/or 124b disposed underneath the micromirror on opposite sides of the structural linkage 108. Hard stops 120a and 120b are provided to stop the action of the micromirror structural film 112.
Energizing the actuator 124a on the left side of the structural linkage 108 causes the micromirror to tilt on the structural linkage 108 towards that side until one edge of the micromirror structural film 112 contacts the left hard stop 120a, as shown in FIG. 1A. Alternatively, the actuator 124b on the right side of the structural linkage 108 may be energized to cause the micromirror to tilt in the opposite direction, as shown in FIG. 1B. When both actuators are de-energized, as shown in FIG. 1C, the micromirror returns to a static position horizontal to the structural linkage 108. In this way, the micromirror may be moved to any of three positions. This ability to move the micromirror provides a degree of flexibility useful in aligning the MEMS device, although the alignment complexity remains significant. Sometimes hard stops 120a and 120b are not provided so that the micromirror structural film 112 is in direct contact with the substrate 104.
For telecommunications applications, optical MEMS devices are typically enclosed within a sealed hermetic enclosure and surrounded by control electronics with accompanying software. A factor in maintaining a high level of reliability for the telecommunications system includes affirming that one or more particular mirrors has switched to the desired position when commanded to route a particular optical signal. One approach that has been proposed to accomplish this is to monitor and detect modulations in the optical power of an optical signal during switching. Other proposals have exploited the fact that in some applications each MEMS device is associated with a particular wavelength, permitting an optical interrogator to be installed for detecting that particular wavelength, and thereby determining that the MEMS device has been switched. A more direct nonoptical approach attempts to sense the MEMS device capacitively after switching, but such sensing is problematic without monolithic integrated on-chip electronics.
There is accordingly a need in the art for methods that permit affirming the switched status of MEMS-based devices.